Multibeam cathode ray tube having a common beam limiting aperture therein

ABSTRACT

An improved multibeam cathode ray tube electron gun is provided wherein a plurality of similar electron beams forming an array pattern are directed to crossover at a common point within the plural beam gun structure. Positioned at the point of crossover is an electrode member having a single aperture therein which uniformly and simultaneously sizes or areally limits each of the individual beams passing therethrough. This reduction in crosssectional area of each beam comprising the pattern array results in a screen pattern array exhibiting markedly improved spot quality and resolution.

uuucu uuuca 1. aucui Say GRUSS REF-R5165 1 1 Mar. 19,1974

MULTIBEAM CATHODE RAY TUBE HAVING A COMMON BEAM LIMITING APERTURE THEREIN Inventor:

Assignee:

Donald L. Say, Waterloo, N.Y.

GTE Sylvania Incorporated, Seneca Falls, N.Y.

Filed:

Y 7 Sept. 14, 1972 Appl. No.2 288,996

U.S. Cl

Int. Cl.

313/70 R, 313/83, 313/86 KM 11013 29/50 Field of Search 313/70, 70 C, 83, 82 BF,

313/82 C, 86 KM References Cited. UNITED STATES PATENTS l 1/1958 12/1965 McNaney 313/86 KM x Schlesinger Dufour 313/82 BF Koda 313/86 KM Kobayashi 3 13/86 KM 2.070.319 2/1937 Rudenberg 313/86 BF X Primary Examiner-James W. Lawrence Assistant ExaminerSaxfield Chatmon. Jr.

Attorney, Agent, or Firm-Norman J. OMalley; Frederick H. Rinn; Cyril A. Krenzer 5 7 ABSTRACT An improved multibeam cathode ray tube electron gun is provided wherein a plurality of similar electron beams forming an array pattern are directed to crossover at a common point within the plural beam gun structure. Positioned at the point of crossover is an electrode member having a single aperture therein which uniformly and simultaneously sizes or areally limits each of the individual beams passing there- 7 through. This reduction in cross-sectional area of each beam comprising the pattern array results in a screen pattern array exhibiting markedly improved spot quality and resolution.

6 Claims, 7 Drawing Figures 6/1960 McNaney 313/86 KM PATENTEDMAR 1 9 I974 SHLEI 1 UP 2 GOVERNMENT CONTRACT I The invention herein described was made in the course of or under a contract or subcontract thereunder, with the Department of Defense.

BACKGROUND OF THE INVENTION This invention relates to multibeam cathode ray tubes and more particularly to an improvement in a multibeam cathode ray tube electron gun structure having uniform beam limiting means therein.

In certain types of high resolution cathode ray tubes, such as those used in alpha numeric, mapping or graphing presentations or in film recording applications, it has been found advantageous to employ a multibeam tube having a plurality of substantially parallel and separately modulated electron beams, such as for example, 20 to 60 individual beams, arranged in a discrete pattern array. To achieve a multibeam pattern of the desired size in a tube of reasonable dimensions, it has been found expedient to use a compact electron gun structure partially comprised, for example, of a common emission plane and several parallelly related planar electrodes having a multiplicity of aligned apertures therein. Multiple beam tubes, in addition to exhibiting increased writing speed, usually have the capabilities of improved brightness and enhanced resolution. But, in those applications wherein it is desired to have a demag-nified or reduced areal display pattern, such as that employed in recording applications, haze surrounding the individual beams in the pattern array sometimes develops to be a significant detracting factor in the quality of the screen display.

The presence of surroundinghaze is resultant from the fact that all electron beams have less than perfect collimation upon leaving the region of the electron gun, such being due to several factors such as: area of beam source, inaccuracies in gun electrode alignment, and space charge repulsion in the beams. In multiple beam tubes, of the type described, influences of the radial components'rof beam velocity are particularly noticeabledue to an extended low velocity drift space in the forward portion of the gun structure wherein the forward component of beam velocity permits some degree of radial divergence of the rays comprising the beam. As a result, when the individual beams reach the region of the focus coil, they may each be as large as inch in diameter. It is exceedingly difficult to focus beams of such diameters to effect the small spot sizes required to produce the reduced pattern array of desired quality. Spherical aberration in the focusing lens promotes the haze condition surrounding each of the beams, which in turn, excites spurious luminous emission of the screen phosphor material peripheral to the core of the focused spot. Thus, this detracting background haze, surrounding the screen impingement of the plural beams, becomes a major concern in a closely spaced imaged pattern.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the invention to reduce the aforementioned disadvantages and to provide a multibeam 2 A further object is to improve the spot quality of the screen pattern array in a multibeam tube by forming each of the screen-impinging electron beams to a substantially uniform diameter and size to prevent overlapping influence in the array pattern display.

These and other objects and advantages are achieved in one aspect of the invention by providing a multibeam cathode ray tube having an electron gun structure wherein a plural array of beams emanating from similar emission areas are controlled, accelerated and collimated by a plurality of sequentially related electrodes which direct the array of beams to impinge and focus on the cathoduluminescent screen of the tube. Within the gun structure forward of the accelerating electrode, there is a crossover point of the plural beams comprising the array. At substantially this crossover point there is positioned a beam-limiting electrode member having a single aperture therein which uniformly and simultaneously sizes or limits the cross-arealsize of each beam passing therethrough. These size-limited beams provide markedly improved spot quality of the resultant screen cathode ray tube electron gun capable of presenting an improved screen pattern array.

pattern array.

BRIEF DESCRIPTION OF TIIE D AwINos FIG. 1 is a view of a multibeam cathode ray tube indicating the location of the invention;

FIG. 2 is a diagrammatic cross-sectional view of pertinent electrical portions of a multibeam tube utilizing the invention;

FIG. 3 is an enlarged prior art elevational view of a cut-away portion of the face panel of the tube illustrating the impingement of two spaced-apart large electron beams on thescreen portion thereof;

FIG. 4 is an enlarged prior art view taken along the line 4-4 of FIG. '3 illustrating a portion of the screen pattern array of large electron beams impinging the screen;

' FIG. 5 is an enlarged cross-sectional view of the beam-limiting aperture of the invention;

FIG. 6 is an enlarged elevational'viewof a cut-away portion of the face panel of the tube showing two spaced-apart limited beams, resultant from the invention, impinging the screen thereon; andv FIG. 7 is an enlarged view taken along the line 7'7 of FIG. 6 illustrating a portion of the screen pattern array of the limited beams resultant from the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT specification and appended claims in connection with the aforedescribed drawings.

With reference to the drawings, there is shown in FIG. 1 an example of a multibeam cathode ray tube 11 of a type utilized in film recording, having a longitudinal axis 13 therethrough and an envelope 15 which includes a face panel or viewing portion 17, a funnel portion 19, and a neck portion 21. Suitably disposed on the inner surface of the face panel 17 is a cathodoluminescent screen 23. Positioned within the neck portion of the tube 21 is a multibeam single electron gun structure 25 which is fabricated to produce an array of plural beams 27 which are directed to impinge the screen 23.

Electrical conductive means are applied to the interior surface of the neck 21 and funnel l9 portions of the tube envelope to effect an electrical connection between the electron gun structure 25 and the screen 23. The first electrical conductive means beyond the gun structure 25 is in the form of a spiral accelerator or resistive helix.29 which is applied to the inner surface of the neck portion 21 in a manner to extend from the gun structure 25 to the internal conductive coating 31 disposed on the interior surface of the funnel portion 19. Extending forward therefrom is an interiorly applied metallic coating 33 which completes the electrical connection with the screen 23.

To ensure that the beam pattern array 27 impinges the screen 23 in desired alignment, an alignment coil 35 is normally exteriorly positioned on the tube neck portion 21. Forward therefrom there is exteriorly mounted an astigmatism correction coil 37 in proximity to the magnetic focus coil 39 which is mounted at the high voltage end of the helix 29. The focus coil has a plane 41 extending therethrough. A deflection coil 43 is formed to encompass the envelope transition region where the funnel portion 19 joins the neck portion 21.

The multibeam electron gun structure 25 has a number of symbolically shown externally extending electrical connections 45 which are normally brought out through the base portion of the tube 47. Within the gun structure there is a planar member having a single beam-limiting aperture 48 therein which is referenced by the plane 49.

To provide greater detail of the invention, FIG. 2 shows a diagrammatic cross-sectional view of pertinent elecrical portions of the multibeam tube 11 illustrated in FIG. 1 with the encompassing envelope substantially omitted. In conjunction therewith, additional clarity is provided by FIGS. 5, 6, and 7 which are portional views related thereto.

By way of example, a tube representative of this type of construction is one capable of presenting a thirty beam array pattern, the lateral dimension of the face panel being in the order of 6 inches and the overall length of the tube being substantially inches.

The multibeam electron gun of the tube type described employs a basic structure 51 wherein the individual electron beams are generated, controlled, accelerated and collimated. Such structure is of known construction, such as for example, a stacked integration of spatially related parallelly oriented planar electrode members. More specifically, the basic gun structure may comprise of a common thermionic emission plane or cathode in the form of a tubular member 53 having electron emissive material 55 suitably disposed thereon; Spaced from and parallel with the emission plane, and substantially normal to the axis 13, is a planar control electrode mat 57 having a plurality of provisions for individually controlling the separate electron beams emanating from the common emission plane 53. Spaced from and substantially parallel with the control electrode mat 57 and aperturally aligned therewith is at least one plural-apertured planar electrode mat 59, which functions as an acceleratingcollimating electrode. Usually two or more of these electrode mats are employed to achieve efficient collimation of the plural array of electron beams involved.

Forward of the terminal planar electrode 61 and electrically isolated therefrom are three separate sequentially positioned coaxial lens cylinders, of which the first lens-forming electrode 63 is in the form of a cylindrical member normally having a diameter larger than the lateral dimension of the basic gun structure 51. Anterior to the first lens-forming electrode, and spaced therefrom, is the second cylindrical lensforming electrode 65 which is operated at a potential significantly differing from that of the first lensing electrode 63. The terminal electrode of the electron guns is the third cylindrical lens-forming electrode 67 which is normally electrically isolated from the second lensforming electrode and, depending upon the desired lensing action, operates at a near or somewhat differing potential. Within this third lens-forming electrode is a planar beam-limiting member 69 having a single aperture 48 oriented substantially axially therein, and being structurally related to the third lens forming electrode, it thereby operates at the same potential. Forward of the terminal electrode of the electron gun and electrically connected thereto is the low voltage end 28 of the helix 29. In turn, the opposed high voltage end of the helix is electrically connected to the internal conductive coating31 which makes connection with the screen 23 through the contiguously disposed metallic coating 33. The external high voltage connection 71 for the screen end of the tube is usually made to the conductive coating 31.

In the tube embodiment described for use in film recording applications, it is desired to focus the gunformed beam pattern array to a reduced or demagnified image on the screen. For example, it is a desideratum to reduce the multiple 30 beam pattern, maximally dimensioned in the gun at substantially 0.348 inch, to a screen array dimension of substantially 0.030 inch, such representing an approximate 12 to l demagnification ratio. In achieving minimization of the array pattern, it was found that miniaturization in the gun structure per se is not efficiently feasible beyond reasonable dimensioning. For instance, the minimum pitch between adjacent beams in the control electrode mat 57 was found to be substantially 0.012 inch. Attempts to reduce this pitch to 0.009 inch resulted in unreliable gun parts. Therefore, the effective demagnification of the array pattern is influenced by both the structural design and operational considerations of the tube as will be subsequently explained.

Operationally speaking, the first lens-forming electrode 63 has a low potential applied thereto, as for example, in the vicinity of zero volts. In contrast therewith, the second lens-forming electrode 65 is operated, in this instance, at a potential in the order of 60 volts; and the third lens-forming electrode 67 may be operated at a somewhat higher or lower potential dependent upon the degree of demagnification required. Thus, there is a modified drift space or region of low potential influence on the plural beams substantially existent in that portion of the gun between the terminal planar electrode 61 and the mid region of the third lens-forming electrode 67. The degree of demagnification of the plural beam pattern that occurs in this drift space region is influenced by the shape of the convex field lens extending from the accelerating helix into the drift space region.

With further reference to FIG. 2, the array of plural beams 27 are shown emanating from the terminal electrode 61, such array being controlled and directed to a first crossover point 73 within thev third lens-forming electrode 67, whereat the beam-limiting aperture 48 is positioned. For purposes of simplification only the central rays of the extremital beams 75 and 77 of the array pattern are delineated. These array-defining beams, upon penetrating the influencing field of the helix, are subjected to a second crossover at point 81; and upon the influence of the focus coil 39, as referenced by the plane of the focus coil 41, are again brought to a third crossover point 83 nearer the screen.

To appreciate the importance of the beam limiting aperture 48, attention will first be given to the prior art situation wherein the common limiting aperture is not utilized. In the prior art operation, the low forward component of velocity influencing each of the plural beams in the drift space region allowed an extended period of time during which radial divergence of the individual beams materialized. Thus, when the separate beamscomprising the pattern array reached the plane of the focus coil 41 they had greatly increased in size, some being as large as a half inch in diameter. To focus a beam of this diameter to a screen spot size of 0.0007 inch diameter is a Herculean task even when utilizing the best magnetic focus lenses available. Spherical aberration in the focusing lens promotes an annoying haze condition surrounding each of the enlarged individual beams. Reference is made to FIGS. 3 and 4, wherein an enlarged prior art elevational view illustrates the screen impingement of two spaced-apart relatively large extremital beams 75' and 77 definitive of the prior art pattern array 85 partially defined in FIG. 4. The large beams 75' and 77' crossover at 83 in cross.- over plane 84 and impinge the cathodoluminescent screen 23 exciting the respective spot areas 87 and 89' representing spot dimensions of (a') and (b) respectively. The sleeves of peripheral haze 91 and 93' surrounding the beams 75 and 77' respectively individually crossover along their respective beam paths in haze crossover plane 95 and thence impinge the screen 23 spuriously exciting areas 97 and 99 dimensioned as (c') and ((1') respectively. It is to be noted in referring to FIG. 4 that each haze excited area covers a plurality of adjacent spots. Thus, when recognizing 'that each of the beams presents a similar extensive and overlapping condition, the magnitude of the haze influence, in detracting from the resolution and brightness of the pattern display, readily becomes apparent.

It was found that a beam-limiting electrode member 69 strategically positioned at the first crossover point 73 within the third lens-forming electrode 67 would effect a profound .improvement in screen spot size. With reference to FIG. 5, an enlarged portion of the beamlimiting electrode and its axially oriented beam-limiting aperture 48 are illustrated. The aperture 48 per seis substantially round and preferably infundibular in shape. It is preferably positioned relative to the direction of electron beam travel with the larger diameter (e) of the aperture shaping, defined by the larger periphery 101, being oriented toward the screen of the tube. The effective peripheral edge 103 functions as the primary beam-sizing opening or minimum annular area and should be free of protuberances that would deform the beam passing therethrough. It is preferred to have the peripheral edges of the aperture smooth and slightly rounded. If the aperture 48 was positioned in the opposite manner, i.e., with the effective peripheral edge 103 oriented toward the screen, portions of the large incoming beam would strike the infundibular slope of the aperture causing spurious ray deflections and the impact release of deleterious secondaries which, being so far removed from the screen, would result in the emission of a general detractive haze emission on the screen.

With further reference to FIGS. 1, 2, 5, and 6, as previously described, the beam-limiting aperture is positioned at the region in the gun structure where all of the electron beams of the pattern array 85 crossover. To expedite explanation only one beam will be described in its relationship to the aperture 48. The emitted beam in traversing the aforedescribed modified drift space region within the gun may have an exemplary diameter (f) in the order of 0.250 inch. In passing through the effective periphery 103 of the aperture, de-

fined in this instance by a diameter (g) of substantially 0.080 inch, the beam is effectively cooky-cut to a like diameter (h) which represents the denser or core portion of the beam wherein the central bundle of rays is designated by (r). Two of the limited beams 75 and 77, which are representative of the extremital beams of the pattern array 85, are further delineated in FIGS. 2 and 6. The limited or smaller diametered beams, being composed of the denser or core portions of the original beams, have less peripheral haze encompassments 91 and 93. Therefore, when the beams make excitive impact with the screen and effect discrete spot areas 87 and 89, as evidenced by diametrical dimensions (a) and (b), there areminimal or negligiblehaze areas 97 and 99 having unobtrusive diameters of (c) and (d) respectively. The screen pattern array evidences small spot sizes (c) which are in the order of 0.0007 inch, wherewith there are associated insignificant surrounding haze corona diameters (d) of approximately 0.002 inch. Since a typical spacing (k) between spots may be in the order of 0.003 inch, there is no deleterious overlapping of the trivial haze influences in the display. In contradistinction thereto, in the prior art situation wherein there was no beam limiting aperture, the size of each individual beam at the plane of the focus coil 41 was approximately 0.500 inch with a final focused beam spot of around 0.001 inch. It is known that the spherical aberration of the lensing associated with the focusing coil 39 increases as the third power of the offaxis distance (m) of the beam from the tube axis 13 at the plane of the focus coil. Therefore, if a representative la'rger beam 75' has a beam diameter in the order of 0.500 inch at the plane of the focus coil 41, which diameter being four times the diameter of a representative limited beam 75, at the same location, the excited haze area surrounding the larger spot in the screen may be 64 times larger than the haze area surrounding the limited beam spot.

In addition to physically limiting the sizes of the beams passing therethrough, it was found that the potential of the limiting aperture is effective in controlling the size of the imaged screen pattern array. It is thought that this pattern size control is resultant from the influence of the aperture voltage affecting the potential over much of the length of the modified drift space. For example, as the aperture voltage is increased, drift space demagnification diminishes and the size of the imaged pattern array on the screen increases accordingly. For instance, where an aperture potential of substantially 65 volts produces a 0.030 inch maximum screen image, an increase in the aperture potential to substantially 175 volts results in producing a maximum screen image of substantially 0.060 inch.

As in most magnetic focusing fields, the bundle of electron beams comprising the pattern array is subjected to rotational influences as well as focusing. This rotation may be in either a clockwise or counterclockwise direction depending upon the direction of the current through the focus coil. in a thirty beam array tube, the pattern rotation was found to be 50 to 55. To properly orient the array pattern with respect to the lateral axes of the screen, the gun structure is axially rotated in the neck of the tube during tube manufacture. Since the beam limiting aperture 48 is axially oriented in the gun structure, this corrective axial rotation of the gun in no way affects the intended and beneficial functioning of the common limiting aperture.

Thus, there is provided a marked improvement in a multibeam cathode ray tube electron gun the result of which is an enhanced screen pattern array exhibiting better resolution and controlled brightness. The beamlimiting aperture in the electron gun structure provides discretely defined beams which produce a screen array of smaller uniform spot sizes that exhibit a minimum of background haze.

While there has been shown and described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. An improvement in a cathode ray tube multibeam electron gun having therein a common emission plane, a parallelly related planar arrangement of separate control electrode members defining an array of individual electron beams, at least one accelerating-collimating electrode plane, a plurality of substantially cylindrical electron lens-forming electrodes, and a terminally oriented spiral accelerator sequentially positioned forward thereof to effect a plurality of sequentially spaced common crossovers of the beams in directing the array of beams to impinge and focus on the cathodoluminescent screen of said tube in a controlled predetermined manner, said electron gun improvement including means for discretely controlling the sizes of the individual beams comprising:

a planar beam-limiting electrode member positioned at the area of the first crossover of said plural beams within one of said cylindrical lens-forming electrodes, said beam-limiting electrode having a single aperture oriented substantially axially therein at substantially a point of crossover of the plural beams in said lensing electrodes to uniformly and simultaneously limit the cross-areal size of each beam passing therethrough.

2. The improvement in the multibeam electron gun according to claim 1 wherein said beam-limiting aperture has a peripheral edge of substantially minimum annular area free of protuberances.

3. The improvement in the multibeam electron gun according to claim 1 wherein said beam-limiting aperture is substantially round.

4. The improvement in the multibeam electron gun according to claim 1 wherein said beam-limiting aperture is substantially infundibular in shape with the larger diameter of said shaping being oriented toward said screen. structure,

5. An improvement in a cathode ray tube multibeam electron gun having anaxis therethrough and a terminally oriented electron beam acceleration means wherein said plural beams emanate from similar emis sion areas and have separate control electrode members defining an array of individual electron beams and a common accelerating electrode member with separate apertures therein, said plurality of beams having a common crossover point within the gun structue, said improvement comprising:

a beam-limiting electrode member positioned in a lens forming electrode forward of said common accelerating electrode, said beam-limiting electrode having a single aperture oriented relative to said tube axis at substantially the first point of crossover of said array of plural beams to uniformly and simultaneously limit the cross-areal size of each beam passing therethrough.

6. An improvement in a cathode ray tube multibeam electron gun according to claim 5.wherein said beamlimiting aperture is substantially round and infundibular in shape. 

1. An improvement in a cathode ray tube multibeam electron gun having therein a common emission plane, a parallelly related planar arrangement of separate control electrode members defining an array of individual electron beams, at least one acceleratingcollimating electrode plane, a plurality of substantially cylindrical electron lens-forming electrodes, and a terminally oriented spiral accelErator sequentially positioned forward thereof to effect a plurality of sequentially spaced common crossovers of the beams in directing the array of beams to impinge and focus on the cathodoluminescent screen of said tube in a controlled predetermined manner, said electron gun improvement including means for discretely controlling the sizes of the individual beams comprising: a planar beam-limiting electrode member positioned at the area of the first crossover of said plural beams within one of said cylindrical lens-forming electrodes, said beam-limiting electrode having a single aperture oriented substantially axially therein at substantially a point of crossover of the plural beams in said lensing electrodes to uniformly and simultaneously limit the cross-areal size of each beam passing therethrough.
 2. The improvement in the multibeam electron gun according to claim 1 wherein said beam-limiting aperture has a peripheral edge of substantially minimum annular area free of protuberances.
 3. The improvement in the multibeam electron gun according to claim 1 wherein said beam-limiting aperture is substantially round.
 4. The improvement in the multibeam electron gun according to claim 1 wherein said beam-limiting aperture is substantially infundibular in shape with the larger diameter of said shaping being oriented toward said screen. structure,
 5. An improvement in a cathode ray tube multibeam electron gun having an axis therethrough and a terminally oriented electron beam acceleration means wherein said plural beams emanate from similar emission areas and have separate control electrode members defining an array of individual electron beams and a common accelerating electrode member with separate apertures therein, said plurality of beams having a common crossover point within the gun structue, said improvement comprising: a beam-limiting electrode member positioned in a lens forming electrode forward of said common accelerating electrode, said beam-limiting electrode having a single aperture oriented relative to said tube axis at substantially the first point of crossover of said array of plural beams to uniformly and simultaneously limit the cross-areal size of each beam passing therethrough.
 6. An improvement in a cathode ray tube multibeam electron gun according to claim 5 wherein said beam-limiting aperture is substantially round and infundibular in shape. 